Natural killer (NK) cells use killer cell immunoglobulin-like receptors (KIR) to distinguish normal cells from infected and malignant cells. NK cells express an apparently random assortment of KIR genes. Our LONG RANGE GOAL is to use NK cells to treat cancer and infectious diseases. Our CURRENT OBJECTIVE is to identify how developing NK cells initiate and then maintain selective KIR gene expression. Supported by strong preliminary data, our CENTRAL HYPOTHESIS is that promoter methylation controls locus-specific and allele-specific KIR gene expression. The RATIONALE for the proposed research is that understanding KIR gene regulation could lead to effective immunotherapy of cancer and infectious diseases. Furthermore, our research will test the central paradigm of tissue-specific gene expression. The proposed research is a COLLABORATION between investigators at two universities. The principal investigator has an established record of research in NK ceils, immune recognition of HLA class I molecules, and molecular biology. The other investigators are leaders in gene expression control and in human NK cell development. The collaboration will produce a synergistic effect that is not easily matched by a single investigator. Our SPECIFIC AIMS are to 1. Test the molecular mechanisms of KIR gene expression control. 2. Define cis acting elements and trans-acting factors that control KIR gene expression. 3. Elucidate how developing NK cells initiate selective KIR gene expression. Our approach is INNOVATIVE. We have produced unique new data and we will combine several cutting-edge research techniques to rigorously test our hypotheses. It is our EXPECTATION that 1) we will develop a clear understanding of how NK cells maintain stable KIR expression; 2) we will define several important cis-acting elements and trans-acting factors that regulate KIR transcription; 3) we will identify what signals developing NK cells use to initiate KIR gene expression. Our results will be highly SIGNFICANT, because they will be essential for understanding how NK cells distinguish normal from aberrant cells. Of broader significance, elucidation of KIR gene expression control will provide an important model for gene choice in development and offer insights into birth defects and cancer.